Dry cell



H` W. FORTH Jan. 5, 1932.

DRY CELL Filed May 21, 1929 Fatented dan. 1932 stares sarai-rr ortica HENRY W. PORTE, OF MADISON', WISCONSHE, ASSIGNB. T@ BURGESS BATTERY GGM- lm, 0F MADISON, WISGONSIN,A

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rlhis invention relates to an'improved dry cell.

It is an object of this invention to improve the performance of a dry cell both on shelf and on dischar e.

A dry cell o the Leclanch type may be made in several ways but usually has a gelatinous ilm or a paper pulp separator between the zinc or negative electrode and the depolarizing mix. The cells may be either of the round or fiat types. Fig. 1 illustrates in cross section the I.round type of cell having a gelatinous electrolyte while Fig.' 2 *illustrates in cross section the round type with a paper pulp separator. A

In a gelatinizd paste cell a depolarizing mix 1 consisting of magazine dioxide, carbon or graphite, sal ammoniac and zinc chloride is molded around a central carbon electrode 2 which has a brass cap 3. Thev molded mix and carbon, yusually called a core, may have an insulating bottom 4 attached to it and a bibulous/ wrapping of cheesecloth 5 is arranged around it. Agelatinous'electrolyte 6 'surrounds the `core sind forms a conducting.v path from the 'core to a zinc can or `anode 7. A wax or pitch seal 8 rests on a washer 9 in the top of the can and the washer is spaced from the top of ,the core to form an expansion space 10.

In the paper pulp lined type of cell, Fig. 2, a zinc can 11 has a paper pulp lining 12. The depolarizing mix 13 is tamped in place around the carbon rod 14 which has a brass cap 15. Sand and sawdust 16 cover the top of the depolarizin mix. A wax or pitch seal 17 forms the cell c osure.

Dry cells are used for a large variety o urposes. Under some conditions a cell may e discharged rapidly and under others it may be discharged slowly, either continuously or intermittently; the discharge period sometimes extending over a period of a year or more. The `cell may be idle for a long period of time in the consumers possession or it may be `idlefor along period on a dealers shelf before being sold and put into service. It is very objectionable for a dry cell to deteriorate or lose its strength during these pe riods of idleness.

iaaa. semino. scarce.

rihle dry cell industry'has striven `for years to overcome such objection and has met with \varying degrees of success. llt is the object of this invention to provide a dry cell which advances another step of this purpose.

It has been known to the art for a long time that mercury or a mercur salt has a in the accomplishment beneficial eiect upon the life o' a dry cell..

' Ihe mercury amalgamates with the zinc and it apparently is this action which produces the benecial effect. Likewise, chromic acid or a salt of chromic acid prolongs the shelf life as described in U. S. Patent No. 1, 331,87 7, issued February 24, 1920. The CrOs radical seems to form a protective ihn on the zinc surface which prolongs the life of the cell when on open circuit.

Although both mercury and the CrOs radical produce beneficial effects separately I have found that by the combination of the two the effect is more than additive. I have found that a cell containin both of these ingredients shows a remarkaly long life when put on light intermittent discharge. This type of discharge is the ty e encountered in the B and .C circuits of ra io apparatus.

I have not been able to determine the cause of the remarkable-results obtained on light intermittent discharge but I have made observations which may' give some clue to the explanation. 'If a mercur salt lis introduced into the dry cell, pre erably by introducing it into the gelatinous electrolyte containing zinc chloride, ammonium chloride, water and a gelat-inized starch as exemplified b Hambuechen Patent No. 1,292,764, issued anuary 28, 1919, but without the CrO. radical present, the zinc soon becomes darken ed due to the amalgamation of the mer-` cury with the zinc. If the chromic acid radical is introduced along with the mercury salt I have discovered that this amalgama- I tion is prevented almost entirely except over long periods of time and on discharge. The e from attacking the 'zincrapidly thus slowing -uppthe amalgamation. Another explanation is that the mercury may unite withpthe (lr03 radical to form mercuric chromate which is somewhat soluble in the electrolyte and gradually breaks down releasingA mercury nto effect the slow amalgamation of the zinc. However that may be, the explanation of the beneiicial results obtained appears to lie in the keeping of the zinc surface clean and preventing its rapid amalgamation by the mercu I belleve that the results yobtained demonstrate that a slow amalgamation during the slow discharge of a cell is much to be preferred `to the rapid amalgamation which is obtained when mercur 1s used in the absence of the CrOa radical.

For the most successful attainment of the above described improved qualities in a dry' cell, mercury should be present in the amount of from 0.00004 to 0.0006 grams and the (lr03 radical in the amount of from 0.00004 to 0.002y grams per square centimeter of zinc exposed to the electrolyte. I prefer to use mercury inthe amount of 0.00008 to 0.0003 grams and the CrO's radicalin the amount Iof 0.0001 to 0.001 grams per square centi? meter of zinc exposed to the electrolyte. I

also prefer having CrOs resent in an amount equal to at least the c emical equiva lent of the mercury in the cell.

Mercury may be successfully introduced in many forms, as metallic mercury or any salt of mercury. My preferred form is mercuric chloride. may be introduced in various forms, as

lchromic acid or any alkali or soluble salts of chromic acid. I prefer to use sodium dichromate.

The method of introducing the mercury/ and CrOa radical should be designed to best meet the conditions. The mercury salt and the Cros radical may be added to the electrolyte at any time before gelatinization occurs in the amounts of about .01% to .2% of mercury salt calculated as metallic mercury and .01% to .5% of the CrOa radical calculated as such. This will usually result in about the correct amount of mercury and CrOs' radical but these amounts must be kept within the limits based upon surface of zinc exposed to electrolyte as above set forth. Best results are obtainedwhen thc mercu is present in from .025% to .10% of thelliynished electrolyte ,and the (lr03 radical in from .025% to .25%.

In the paper pulp lined type of cell as illustrated by Fig.I 2 the active depolarizing mix 13 usually contains.. the mixed chloride of ammonium and;W ziic in the desired v amounts as is familiar all who are skilled Likewise the CrOa radical the mercury.

aqueous suspension of starch may be vemployed to moisten the paper pulp liningv 12 prior to its insertion into the can 11. The mercury and CrOs radical in the amounts 'hereinbefore `specified maybe introduced in the water or in this suspension. In both of thev above described t pes of cells, the CrOa radical in the form ofy a salt and mercury in the metallic form or as a salt can be conveniently incorporated in the .active depolarizing mix. Other methods for introducing these materials will become apparent to those skilled in the art.

Although I prefer to introduce the CrO, radical and mercury into the cell bydissolving salts of these two materials in the electrolyte or by introducing them into the mix or paper partition, as hereinbefore described, it 1s also possible to mix l"the mercury and Cros, salts before introducing them into the cell thereby forming a mercury salt of chromic acid.. It is possible to use this mercury salt of chromic, acid in the same manner as the separate salts were used before they were combined. Throughout the specification and claims I do not wish tobe restricted to adding the chomic acid radical and the mercury salt separately to the electrolyte but I also include the formation of a mercury salt of chromic acid prior to its addition to the cell.

This application is a continuation, in part, of my copending application, Serial No. 235,768, led Nov. 26, 1927.

I claim: A A

1. In a dry cell comprising a zinc anode, a carbon cathode, a depolarizm mixture arranged between the anode an cathode, and a nonacid electrolyte; a. mercury salt and CrOs radical operatively associated with the electrolyte.

2. In a dry cell comprising a zinc anode, a carbonl cathode, a depolarizmg mixture arranged bctween the anode and cathode, and a non-acid electrolyte; mercurio chloride and a salt of'CrOs in the electrolyte. A

3. In a dry cell comprisinga zinc anode', a

carbon cathode, a depolarlzlng mixture arranged between the anode and cathode, and a non-acid electrolyte; mercuric chloride and sodium dichromate in the electrolyte.

4. In a dry cell comprisin a zinc anode, a carbon cathode, a depolarizmg mixture arranged betweenthe anode and cathode, and a non-acid electrolyte; a mercury salt and at least enough salt of chromic acid Vin the electrolyte to retard amalgamation of the zinc can .b the mercury. y

5. yn a dry cell comprisin a 'zinc anode, a carbon cathode, a depolarizmg mixture arranged between the anode and cathode, and a non-acid electrolyte; mercuric chloride and at least enough dichromate'in the electrolyte to retard amalgamation of the zinc canby memes 'to .0006 grams of mercury in the mercury salt per square centimeter of zinc exposed to said electrolyte and substantially .00004 to .002 grams of the OrO, radical per square centimeter of zinc exposed to said electrolyte.

8. A dry cell having a zinc anode and containing in its electrolyte substantially .00008 to .0003 grams of mercury in the form of a meren? salt per square centimeter of zinc expose to said electrolyte and substantially .0001 to .001 grams of the CrO, radical er square centimeter of zinc exposed to said e ectrolyte.

9. An electrolyte paste for a dry cell containing from substantially .01% to .2% mer cury in the form of a mercury salt `and from suantially .01% to .5% of the CrO, radica 10. An electrolyte paste for a dry cell containing from substantially .025% to .1%. mercury in the form of a mercu salt and from siistantially .025% to .25% o l the CrOs radic In testimony whereof I ax m si ature.

' HENRY W. OTH

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